The present invention relates to data processing.
In electronics, a digital-to-analog converter (DAC) may be denoted as a device for converting a digital (usually binary) code to an analog signal. Digital-to-analog converters are the interface between the abstract digital world and the analog real life. Simple switches, a network of resistors, current sources or capacitors may implement this conversion. An analog-to-digital converter (ADC) performs the reverse operation.
Engel Roza “Analog-to-Digital Conversion via Duty-Cycle Modulation”, IEEE Transactions an Circuits and Systems—II: Analog and Digital Signal Processing, Vol. 44, No. 11, 1997, pp. 907 to 914 discloses an asynchronous sigma-delta modulator ADC.
U.S. Pat. No. 6,087,968 discloses an analog to digital converter comprising an asynchronous sigma-delta modulator generating an asynchronous duty cycle modulated square wave, sampling means to synchronously sample the asynchronous square wave and a decimating digital filter to convert the samples from the sampling means into a desired PCM-format (Pulse Code Modulation).
U.S. Pat. No. 5,396,244 discloses a digital-to-analog converter comprising a sigma-delta modulator for generating a 1-bit digital signal modulated synchronously with a clock signal in response to a digital input signal. This modulator is followed by an asynchronous analog sigma-delta modulator for generating a bivalent asynchronously modulated signal in response to the synchronously modulated digital signal. The information in the digital signal from the sigma-delta modulator resides in signal transitions which can appear exclusively at discrete instants defined by the clock signal. The information in the asynchronously modulated signal from the asynchronous sigma-delta modulator is contained in an analog variation of the duty cycle. This means that the signal transitions of the asynchronously modulated signal are not tied to a fixed pattern of discrete instants but that all the intervening instants are also available.